1. Field of the Invention
The present invention relates to generating phosphorus (P) fertilizers using microbial fermentation technology, and more particularly by converting phosphate sources to more chemically reduced forms of phosphorus by anaerobic microbial fermentation, with the end products being suitable for use in agriculture.
2. Description of the Prior Art
Phosphites (also known as phosphonates) are a natural component of the phosphorus cycle in soil, plant and marine plant systems. They are defined as the salts of phosphorous acid (H3PO3). Hypophosphites are the salts of hypophosphorous acid. In the following description of this invention, the term phosphite will sometimes be used to describe these salts of phosphorous/hypophosphorous acid. In modern agriculture the phosphorus cycle can be severely disrupted by the widespread use of biocides and inorganic fertilizers. These factors often result in phosphorus limitations in many agricultural soils. In addition, it is known that phosphate based fertilization is not very efficient in many soils due to fixation and adsorption. Moreover, foliar absorption of phosphate is also very poor or non-existent.
Phosphites have been known for some time to have activity in both plants and microbes as sources of plant nutrients (Lovatt, U.S. Pat. No. 5,514,200) and as biocidal agents (Thizy, U.S. Pat. No. 4,075,324) and are now well established in terms of their agrochemical usage. It has also been determined that phosphite-based phosphorus fertilizers demonstrate superior penetrating abilities across plant foliage, and have a propensity to remain more available in the soil and not become as fixed or adsorbed—as is the case with phosphate. Phosphite-based fertilizers are also far more efficient at delivering phosphorus than phosphate-based fertilizers due to having one less oxygen molecule, and as such the proportion of “P” in the molecule is correspondingly higher. Phosphites are also much more soluble and less prone to precipitation and soil adsorption. The superior solubility of phosphites is also advantageous in terms of the anion in the salt. Greater solubility of ammoniacal, potassium, magnesium and calcium salts result in more efficient nutritional delivery whether applied to the soil or particularly to the plant foliage than the corresponding phosphate salt(s).
Phosphites have also been shown to exhibit marked activity against certain microbes such as fungi and bacteria and are used as biocides.
Currently the manufacture of phosphorus fertilizers mainly consist of manufacturing the acid and then reacting the acid with certain bases in order to generate a fertilizer salt such as ammonium phosphate, potassium phosphate, potassium phosphite, etc. These methods generally involve highly reactive and generally exothermic reactions. Also many of the reactants are chemically hazardous. Commercially most phosphites are mainly produced through the reaction of phosphorus trichloride and water, a very hazardous and dangerous reaction. Phosphorous acid is extracted from the products of the reaction and purified. It is an expensive and hazardous process. It would therefore be very beneficial if a less hazardous and more efficient process could be found that could produce phosphites/hypophosphites.
Anaerobic microbes are abundant in nature and mediate many complex biochemical reactions in nature. Any environment where oxygen is absent or limiting, anaerobic metabolism can take place. Examples of anaerobiosis can be found in ecosystems such as in marshes and stagnant water bodies where organic matter decomposes in the absence of oxygen and leads to the on formation of ‘marsh gas’. Marsh gas is largely methane. Anaerobic putrefication and degradation of organic matter is usually accompanied by unpleasant odors of hydrogen sulfide and of organic compounds that contain sulfur, such as mercaptans (any sulfur-containing organic compound). In such reducing conditions, oxygen rich molecules are not abundant.